1. Field of the Invention
The present invention relates to an apparatus and a method for guiding a person or an object (e.g., a vehicle) to a specified destination by use of a map.
2. Description of the Related Art
A car navigation apparatus is known as an apparatus for guiding a person or vehicle to a specified destination by using a map (more specifically, by showing a detailed route to the destination). In general, the car navigation apparatus utilizes a GPS (Global Positioning System) and a satellite to determine (detect) a current location of the vehicle. Referring to FIG. 1 of the accompanying drawings, a screen of a display unit 6 of the car navigation apparatus is illustrated. After detecting the current location of the vehicle, the car navigation apparatus superposes a car location mark MC over the detected car location on the map displayed by the display unit 6. When a driver or passenger in the vehicle specifies a destination OM, the car navigation apparatus determines an optimal route OR to the destination OM from the current car location MC, and displays, for example, a red line (indicated by the bold line in FIG. 1) over or along the optimal route. If the vehicle approaches a crossing on the way to the destination OM, the navigation apparatus superposes a heading direction guidance image over the displayed map. The heading direction guidance image indicates which route the vehicle should take at the crossing. FIGS. 2A to 2C of the accompanying drawings are the heading direction guidance images. The images of FIGS. 2A to 2C may be created by a deforming technique. FIG. 2A illustrates the guidance image to guide the vehicle straight. FIG. 2B illustrates the guidance image when the vehicle should turn to the right at the crossing. FIG. 2C illustrates the guidance image to guide the vehicle to the left. These guidance images are prepared beforehand on the assumption that every corner has a turning angle of about 90 degrees. It should be noted that the term “crossing” includes not only a three-way crossing, a four-way crossing but also a roundabout (also known as a traffic circle) in this specification.
However, all the corners on the road are not right angle corners, as understood from the map shown in FIG. 1. For instance, two of the four corners at the crossing K1 are not 90-degree corners. The conventional navigation apparatus includes only the three guidance images shown in FIGS. 2A to 2C.
If the vehicle approaches the crossing K1 on the way to the destination OM, practically no problem will occur because the driver understands that the driver should go a little diagonally, rather than making a 90-degree turn, even if the driver sees the guidance map of FIG. 2A (i.e., “go straight” guidance). This is because there are only three choices at the crossing K1.
On the other hand, if the vehicle is entering a complicated crossing such as a circle or roundabout, there may be four or more directions to choose. In FIG. 1, for example, the roundabout RK has five branching routes, and the vehicle entering the roundabout RK has four routes to choose. The branching routes extend in different directions. FIG. 3 of the accompanying drawings shows another roundabout which has six branching routes and presents five choices. There may be different types of roundabouts on the streets. The conventional car navigation apparatus has only three guidance maps as shown in FIGS. 2A to 2C so that the car navigation apparatus cannot provide the driver with appropriate guidance information when the vehicle approaches the roundabout. It might be theoretically possible to prepare many guidance maps to match all roundabouts on the streets. This is however impractical since a huge amount of image data must be stored.